The present invention relates to a process for modifying polypropylene by means of a grafting reaction with maleic anhydride, in order to obtain a product which can be advantageously used as a compatibilizing agent in the preparation of polypropylene reinforced with glass fibers or mixed with polyamide.
It is known, for example, from the German Democratic Republic patent nr. 275,159, that it is possible to treat polypropylene with maleic anhydride in the presence of peroxide initiators in order to obtain a modified product characterized by improved mechanical properties as well as reasonable adhesion properties.
The use of various peroxide initiators however together with operating conditions which vary in relation to the initiator used, according to the disclosures deriving from the state of the art, causes the formation of products which are not completely homogeneous with each other, also characterized by a degradation degree which makes them unsuitable, or however does not guarantee constant and repeatable use, to be adopted as compatibilizing agents in the preparation of polypropylene reinforced with glass fibers.
The Applicant has now found, and this forms the object of the present invention, that if the modification reaction of polypropylene with maleic anhydride is carried out with dilaurylperoxide and is effected in a solvent-free heterogeneous phase, it is possible to obtain a modified polypropylene whose characteristics enable it to be advantageously used as a compatibilizing agent in the preparation of polypropylene reinforced with glass fiber or mixed with polyamide, without the uncertainties and unreliability described in the general disclosures deriving from the state of the art: furthermore an important factor is the low degradation observed in the products prepared in heterogeneous phase using dilaurylperoxide as radicalic initiator with respect to the products obtained with other methods and other radicalic initiators.
The present invention therefore relates to a process for the grafting of maleic anhydride on polypropylene consisting in reacting the polymer with the anhydride in heterogeneous phase and in the presence of dilaurylperoxide as radicalic initiator.
The reaction is carried out in an inert atmosphere, under nitrogen pressure, at a temperature which progressively rises to a maximum of 110xc2x0 C., for times ranging from 0.5 to 3.0 h. It is finally quenched by the addition of water and, after the removal of the washing water, the product is dried under vacuum. As already mentioned, the reaction is carried out without a solvent, and the grafting yield proves to range from 1.9 to 3.2.
The Following Advantages can be Observed:
the fluidity of the polypropylene is not modified,
as there is no organic solvent, there are no disposal problems of the washing water,
the washings after the reaction are effected with water and sodium hydrate,
high value of grafted maleic anhydride,
insignificant degradation observed on the polypropylene after the reaction,
the product is still completely soluble in hot toluene showing the absence of significant branching and/or cross-linking phenomena.
Using the synthesized products as additives in the preparation of polypropylene reinforced with glass fiber, the evaluation of the physico-mechanical parameters of the end-materials had led to the conclusion that the compatibilization is, in any case, still at a good level of industrial interest.